in the trial you get ARR and Heavensward. im pretty sure once you reach 60 you can just keep playing as much as you want within those parts of the game, you just dont level

to go beyond that you need to buy the base game AND the latest expansion (which are sold together in the Complete Edition). buying the latest expansion gets you access to all the expansions before it

the new expansion is coming out in november, so you might wanna wait to buy the Complete version at that time, and get all 3 of the expansions you have to pay for at once

also apparently purchasing any microtransactions ends the free trial and forces you to buy the game, so... dont do that